Amid concern over carcinogenic styrofoam food containers, the government will issue instructions on how to use the boxes safely, though boxes recently tested in Vietnam came up negative for harmful chemicals.

The instructions would include warnings about not using the boxes to contain food heated to temperatures of over 70 degrees Celsius, and not to put foods with unclear origins into the containers, according to Nguyen Cong Khan, head of the health ministry's Vietnam Food Administration.

The Ministry of Health also planned to cooperate with the Ministry of Industry and Trade to more closely monitor the origins of the disposable containers used in Vietnam, Khan said.

The moves come after the China Daily last month quoted Dong Jinshi, vice-president of the Hong Kong based International Food Packaging Association, as saying that half of the disposable dishware used in China was unsafe, with excessive amounts of chemicals that can cause cancer.

Disposable food boxes have been widely used in Vietnam over the past years and latest reports from authorities showed that there had been lax management over the issue.

However, the latest tests on over 30 samples of containers with Chinese labels in Hanoi showed they didn't contain excessive amounts of chemicals, according to Khan.

The National Lab of Food Safety and Hygiene's previous tests on 50-60 random samples of the containers also found no excessive chemicals.

In the meantime, local newswire Vietnamnet Tuesday quoted Khan as saying that Vietnam would contact related parties before coming to any conclusion on recent information about a brand of orange juice found with thiosildenafil, an analogue of sildenafil, or Viagra, in Malaysia.

The information appeared in a recent issue of Malaysia's New Straits Times and was quoted by several local newspapers and newswires on Monday.

According to the foreign news source, the contaminated soft drink was found at a factory in Seri Kembangan during a raid by the Malaysian Health Ministry last Wednesday.

Malaysian agencies have yet to reveal the drink's brand as well the amount that has been confiscated.